Re: Team 121 Traction Control
 

Kressly beat me to the quote, again.

We are developing our own traction control algothirms. If you PM me, I will hook you up with our code guys to steer you in the right direction...oh, is my GP showing??:o

Re: Team 121 Traction Control
 

All,

Apologies on the slow response, things have been busy in Rhode Warrior Land.

A good number have asked for a better explanation of how we accomplished this traction control, here is the basic outline of what we've done.

The setup includes an encoder in each AndyMark gearbox, as well as two follower wheel assemblies, one for each side of the robot. Through a number of tests, we normalized the follower wheel encoders using a static multiplier so the output would be as close as possible to that of the AndyMark gearbox encoder outputs.

Now we had an accurate idea of both how fast the wheels indicated we were going, and how fast the follower wheels indicated we were going.

A slip ratio can then be calculated by taking the difference between the wheel velocity and the ground velocity, and dividing that by the wheel velocity. Any value that is not zero (or NaN for when the robot isn't moving) indicates wheel slippage. The higher the slip ratio, the more the wheels are slipping.

Feed these values into a tuned PI (Proportional/Integral) loop, to obtain how much the software should "throttle back" each side for various slippages.

A question was asked about how we deal with chain slack/gearbox looseness. To be honest, it was just ignored, and put in the "we'll figure that out later" pile, turns out it seems to handle itself just fine without any modification.

As of now the software is aiming for zero slip. In the coming days we will be testing to see if allowing a little slippage increases our acceleration. For turning I’ve modified the gains such that the software allows a certain percentage slip. The driver also has an "off" button on their trigger, they've grown quite good at using it to kick the robot into a bit of a tail slide, and then keep driving. Anyone who's played the Mario Kart games remembers the "jump->power slide" technique; our drivers seem to love this.

As of right now we've probably put about 10 hours into making this v0 traction control work. I'm confident that we have a few long nights ahead fine tuning this, and making it more competitive.

I would recommend this reading, this is where most of our v0 software was derived from:

http://mizugaki.iis.u-tokyo.ac.jp/st...F/EV_Trans.pdf

Re: Team 121 Traction Control
 

Team 121,
According to the paper (http://mizugaki.iis.u-tokyo.ac.jp/st.../EV_Trans.pdf), you should see a significant traction force increase with very little slip. (Figure 11). This should deliver a significant advantage with trailler pulling. Similiar behavior is exhibited in locomotive applications. Have you been able to verify this? Do you think your control system will be capable of this level of fine tuning?

Re: Team 121 Traction Control
 

That being said, I'd like to thank Tom and 121 for the details they have posted thus far. They basically gave the system away on a silver platter.

As with most projects, writing the code is the easy part. Designing the system is what's tough.

Re: Team 121 Traction Control
 

I'd like to second the thanks to Tom and the team for all the details. We look forward to meeting them in action in both Manchester and Hartford!

Does anyone have any suggestions (or a part number) for an encoder that is suitable for a simple follower wheel application? There are quite a range available, both in resolution and price. Preferably, one with a 1/4" shaft already built in?

Thanks!

Re: Team 121 Traction Control
 

Vex sells a decent encoder that does A/B quadrature. They fit right onto the standard Vex square shaft, and can be interfaced easily to the Vex wheels. You could have something up and running in less than one night.

For a more custom solution, teams have had luck with the Grayhill 61k series of encoders.

Re: Team 121 Traction Control
 

We are using these from BG micro. They are not really designed for this application, but they work gret, and at $4.00 each it's hard to beat!

Here is the spec sheet on them.

Re: Team 121 Traction Control
 

My team is attempting traction control, and a mentor brought up that when we turn we wont be getting the same values with one wheel. I may be just a little bit confused, but we are thinking we will have to do a mouse design with omni wheels to get correct values as we turn. Is this a correct understanding of how this system works?

Re: Team 121 Traction Control
 

I believe 121 is using a similar set up to 148's, which can be seen using an omni-wheel here.

Our team has chosen to use an omni wheel, as well. We will have one follower assembly per side of the robot. We figured it was better to be safe than sorry and used an omni wheel.

Re: Team 121 Traction Control
 

So if im right, teams are using a caster omni wheel to get the turning values along with the straight values?

Re: Team 121 Traction Control
 

also is there a reason why they aren't using the encoder from the kit?

Re: Team 121 Traction Control
 

We are using the kit encoders to get the wheel speed, and omni wheels on each side (not caster mounted) to get the actual speed. We hope to get good results..

Re: Team 121 Traction Control
 

Wonderful work team! Thanks for sharing your psuedo algorithm! You're not giving away your code (absolutely okay), but you are reinforcing the thought scheme so that others can validate their concepts with what actually works. Now that is gracious professionalism.

Re: Team 121 Traction Control
 

Is it slipping on those turns? From the audio it sounded like when it hit the wall it was slipping quite a lot. But I can't be sure just from video & audio

Re: Team 121 Traction Control
 

hey the trailer weighs more and how could you stop